Hi All: I have a question about my E30 M3 (1988). My car has developed a noisy diff, and needs either a rebuild or replacement. First question is any recommendations about a quality diff rebuilder? Any members used one previously with good results? Second, the same diff gear set (4.10:1) came in the 1990-1992 E30 318i and iS cars. Would one of these diffs work as a direct replacement for the E30 M3 diff ? Both came as LSD, standard in the M3, and optional in the 318i/iS cars. BMW no longer supports either model with a new unit, and offers no gear sets to rebuild a worn diff. Any comments or suggestions would be appreciated. My car is original with about 122k miles, so originality of a replacement is important to the car's value.
You should join the E30 M3 SIG (special interest group) - see the links here (https://www.bmwcca.org/special-interest-groups), email Filippo - someone there should know every aspect of what you're asking (at least, I'd expect so). If that route gets you answered, relay back here what you find out. Looking at the cross-listing on realoem.com, shows a lot of other E30 325i models, of course not all are 4:10's... I think you find the 4:10's primarily in the auto-trans cars, including U.S. models; that makes me think the diff housing there is interchangeable, but it's not showing any E30 318's... looking at the same section for U.S. 318is, shows a lot of euro models, smaller displacement M20-engined cars, & the U.S. 318's... but that doesn't tell ya a darn thing about whether the diff's are the same or if it's a different housing or what - http://www.realoem.com/bmw/enUS/par...sg=05&diagId=33_0014&q=33101211843&series=E30
Turner can build a diff to what ever spec you want it to be. I wanna say the 318 had a different case on the diff from the 325's and the 325is had the 4.10 LSD and the 325i didn't have LSD if I am remembering that correctly. https://www.turnermotorsport.com/p-340133-e30-differential-upgrade-custom-options/?pdk=AQEBAQYAAQ
Yeah - limited slip diff was standard on 325is, 318is & M3. 325is manual had 3:73 ratio, maybe auto trans had 4:10.
